1. Field of the Inventions
The present invention relates to a tunnel magnetoresistance effect device and to a portable personal device having a magnetic memory provided with said tunnel magnetoresistance effect device.
2. Discussion of the Background
A magnetoresistance effect element using a ferromagnetic thin film is used in, for instance, a magnetic head, a magnetic sensor, etc. Furthermore, a magnetic random access memory (MRAM) is recently proposed, which comprises a semiconductor substrate having formed thereon a magnetoresistance effect device. The MRAM is attracting attention as a next generation memory device promising high speed operation, high capacity, and non-volatile features.
In the magnetoresistance effect, the electric resistance of the ferromagnet itself changes with its direction of magnetization. Thus, a ferromagnet functions as a memory device because it can record information in accordance with the direction of its magnetization, and the information thus recorded can be read in accordance with the size of the electric resistance.
Recently, in a ferromagnetic tunnel junction having a sandwich structure comprising two ferromagnetic layers with a dielectric material inserted between them as a tunnel barrier layer, a magnetoresistivity ratio of 20% or higher is obtained by the tunnel magnetoresistance effect (TMR effect) (J. Appl. Phys., 79 (1996), p. 4724). A device having a ferromagnetic tunnel junction is denoted as a tunnel magnetoresistance effect device (TMR device).
In a TMR device, the direction of magnetization of one of the two ferromagnetic material layers sandwiching the tunnel barrier layer of dielectric material, i.e., the magnetization fixed layer, is fixed, and by changing the direction of magnetization of the other ferromagnetic layer that is in a magnetically non-coupled state with the magnetization fixed layer, i.e., the magnetization free layer in accordance with the applied external magnetic field, information of either “0” or “1” is recorded thereto. A TMR device having such a structure is called a “spin-valve TMR device”.
To fix the direction of magnetization in the magnetization fixed layer, an antiferromagnetic material layer made of an antiferromagnetic material is provided in contact with the ferromagnetic layer to utilize the exchange coupling between the antiferromagnetic layer and the magnetization fixed layer.
FIG. 1 shows a cross sectional structure of a spin valve TMR device using an antiferromagnetic layer.
Referring to FIG. 1, the structure comprises an antiferromagnetic material layer 101 made of an antiferromagnetic material, having sequentially laminated thereon a magnetization fixed layer 102 made of a ferromagnetic material, a tunnel barrier layer 103 made of a dielectric material, and a magnetization free layer 104 made of a ferromagnetic material.
The magnetization of the magnetization fixed layer 102 is fixed in the direction indicated by an arrow A shown in FIG. 1 by the exchange coupling of the antiferromagnetic material layer 101. In contrast to this, the magnetization of the magnetization free layer 103 changes in accordance with an external magnetization field within a range indicated by arrows B and C shown in FIG. 1. As a result, the electric resistance of the TMR device yields a maximum when the direction of magnetization B of the magnetization free layer 104 is reversely parallel with the direction of magnetization A of the magnetization fixed layer 102, and yields a minimum when the direction of magnetization C of the magnetization free layer 104 is in parallel with the direction A.
A sense current for detecting the electric resistance of the TMR device is applied by a pair of electrodes connected to the upper and the lower planes (i.e., the upper plane of the magnetization free layer 104 and the lower plane of the antiferromagnetic material layer 101 shown in FIG. 1) of the TMR device. The direction of the sense current is perpendicular to the film plane of each of the layers.
The ferromagnetic material used in the magnetization free layer 104 and the magnetization fixed layer 102 is an alloy containing a magnetic metal selected from the group consisting of Co, Fe, and Ni. On the other hand, for the antiferromagnetic material that is used for the antiferromagnetic material layer 101, generally employed is an alloy containing Mn, such as IrMn, PtMn, RuRhMn, etc.
A process for producing a MRAM and the like by employing the TMR device above comprises a heat treatment in a temperature range of from about 300 to about 450° C., such as a film deposition of an interlayer dielectric onto the SV-TMR device by means of CVD, a metal reflow treatment, etc. By applying such a heat treatment, Mn included in the antiferromagnetic material layer 101 of the TMR device easily diffuses into the magnetization fixed layer 102 and reaches the vicinity of the tunnel barrier layer 103. The diffused Mn then lowers the spin polarization ratio of the magnetization fixed ratio 102 and leads to a problematic decrease in magnetoresistivity ratio of the TMR device.
In order to prevent the lowering of the magnetoresistivity ratio from occurring, it has been suggested to insert a metallic layer made of a refractory metal, such as Ta, Ru, etc., into the magnetization fixed layer 102 (Appl. Phys. Lett., 76 (2000) 3792; and Appl. Phys. Lett., 76 (2000) 2424). However, as a result of the studies of the present inventors, it has been found that the metallic elements above cause grain boundary diffusion of Mn at temperatures of 300° C. or higher, and that it is not possible to prevent the diffusion of Mn from occurring into the tunnel barrier layer.
Furthermore, it has also been suggested to insert a layer of a refractory metal into the interface between the antiferromagnetic material layer 101 and the magnetization fixed layer 102 (Appl. Phys. Lett., 76 (2000) 3792). However, as a result of the studies of the present inventors, it has been found that a refractory metal layer provided at the interface between the antiferromagnetic material layer 101 and the magnetization fixed layer 102 not only greatly impairs the fixing of the magnetization of the fixed layer 102, but also raises a concern that the refractory metal itself undergoes diffusion.